This invention relates to graft copolymers of starch-acrylamide or starch-acrylamide-acrylic acid which have the property of producing highly viscous aqueous solutions that are particularly useful in recovering oil from subterranean formations.
After the primary supply of oil in a well has been exhausted it has been a common practice in the past to employ any of several secondary techniques to recover oil from the cracks and interstices in the underground rock formations. One technique has been to flood the well with water so as to displace the oil. In more recent times attempts have been made to add a material to the water to produce an even greater recovery of oil. In another technique a liquid is pumped into the well and maintained under a high enough pressure to fracture the underground rock formations and thereby releasing more oil to be recovered. These two techniques can be enhanced by the incorporation of appropriate materials into the liquid. It is an object of this invention to provide solutions of copolymeric materials which greatly facilitate the oil recovery procedure and increase the amount of oil recovered.